The present invention relates generally to the art of protecting a glass surface from staining, and more particularly to the art of stain inhibiting organic acids.
Glass sheets are typically stacked in face-to-face relationship for handling, transportation and storage. Unfortunately, stacked glass sheets are susceptible to scratches caused by relative movement between adjacent surfaces, and staining caused by alkali buildup between adjacent surfaces which degrades the original colorlessness and transparency of the glass.
It is well known in the art to separate adjacent glass surfaces by interposing sheets of paper between the sheets of glass to protect the glass surfaces. However, the techniques for utilizing paper interleaving are time-consuming and costly. Less expensive means for separating glass sheets are particulate interleaving materials, which include natural products, such as wood flour, and synthetic products such as polyethylene, polystyrene or polyacrylate beads. While these inert interleaving materials provide a measure of scratch protection at relatively low cost, staining remains a significant problem.
U.S. Pat. No. 3,723,312 to Hay addresses the problems of staining and scratching of packaged glass sheets. In place of interleaving paper, Hay proposes the use of dedusted agglomerated salicylic acid in conjunction with an inert particulate separator material, such as wood flour or polystyrene, applied at a rate such that one pound of interleaving material protects no more than 4000 square feet, preferably 1000 to 3000 square feet, of glass. According to Hay, use of agglomerated salicylic acid mixed in equal proportion with inert polystyrene is effective to eliminate staining for nearly as long as interleaving paper with application costs which approximate those for wood flour or methyl methacrylate which have no particular stain inhibiting properties.
U.S. Pat. No. 3,798,112 to Hay also discloses a mixture of dedusted agglomerated salicylic acid and inert separator material, providing a novel method for agglomerating the acid with polyethylene oxide to produce an interleaving material comprising substantially spherical particles less than about 30 mesh which is applied to glass sheet surfaces at a rate of about one pound covering not more than about 4000 square feet. The interleaving material may further comprise an inert particulate separating material such as wood flour, polystyrene or LUCITE.RTM. methacrylate polyester beads in a ratio up to about 4:1 with respect to the agglomerated organic acid.
U.S. Pat. No. 4,011,359 to Simpkin et al discloses an interleaving material for separating glass sheets and protecting them from scratching and staining which comprises a porous, finely divided support material, impregnated with a weakly acidic material, and fine particles of a chemically inert plastic material. The porous support material may be a cellulose material of vegetable origin or a wood flour. The weakly acidic material is a weak organic acid, preferably organic acids having 3 to 10 carbon atoms, and especially adipic, maleic, sebacic, succinic, benzoic and salicylic acids. The inert plastic separator material may be polyethylene, polystyrene, polytetrafluoroethylene or a methacrylate polyester, and preferably has a larger particle size than the acid-impregnated support material. The interleaving material may be applied to the glass by conventional powder applicators.
U.S. Pat. No. 4,200,670 to Albach describes a method for protecting glass sheets during packing, shipping and storing. The method involves applying water, a stain inhibiting material, and dry, finely divided particles of a mechanical separator to the surface of glass sheets, prior to stacking them, in a plurality of sequential steps that produce an adherent coating on each glass sheet, which coating becomes a protective interleaving between facing surfaces when the sheets are stacked. According to one specific embodiment, this is accomplished by applying the water and stain inhibitor to the glass as an aqueous solution of the latter to provide a wet layer on the sheet surface, and then separately applying a dry particulate layer of a mechanical separator to the wet layer. The method can also be carried out by first spraying the glass surface with water alone and then separately applying a layer or layers of a stain inhibitor and a mechanical separator in dry powdered form to the layer of water, or by first applying a mixture of dry powdered stain inhibitor and mechanical separator and then spraying the dry materials with water.